arm64: dts: qcom: sm7225-fairphone-fp4: Switch firmware ext to .mbn

arm64: dts: qcom: sm7225-fairphone-fp4: Switch firmware ext to .mbn

Specify the file name for the squashed/non-split firmware with the .mbn
extension instead of the split .mdt. The kernel can load both but the
squashed version is preferred in dts nowadays.

Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Link: https://lore.kernel.org/r/20240110-fp4-mbn-v1-1-45e7e33b1834@fairphone.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>